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The external anal sphincter (or sphincter ani externus) is an oval tube of skeletal muscle fibers. [1] Distally, it is adherent to the skin surrounding the margin of the anus. [2] It exhibits a resting state of tonical contraction [1] and also contracts during the bulbospongiosus reflex. [3] [4] [5] [6]
The internal anal sphincter, IAS, or sphincter ani internus is a ring of smooth muscle that surrounds about 2.5–4.0 cm of the anal canal.It is about 5 mm thick, and is formed by an aggregation of the smooth (involuntary) circular muscle fibers of the rectum.
Anatomy of the human anus. Frontal section. The anus is the final part of the gastrointestinal tract, and directly continues from the rectum, passing through the pelvic floor. The top and bottom of the anus are surrounded by the internal and external anal sphincters, two muscular rings which control defecation.
The external anal sphincter muscle is the voluntary muscle that surrounds and adheres to the anus at the lower margin of the anal canal. This muscle is in a state of tonic contraction, but during defecation, it relaxes to allow the release of feces. Movement of the feces is also controlled by the involuntarily controlled internal anal sphincter ...
Anal sphincter muscles may refer to: External anal sphincter; Internal anal sphincter This page was last edited on 2 January 2025, at 16:44 (UTC). Text is ...
The rectococcygeal muscles form part of the complex arrangement of muscle surrounding the rectum, sometimes termed the anal-sphincter complex, which act to stabilise and support the anal canal during defecation. The rectococcygeal muscle acts to lift the sphincter, thereby effectively shortening the rectum and aiding evacuation. [5]
The anal triangle is the posterior part of the perineum. ... Sphincter ani externus muscle; ... Anatomy photo:41:01-0202 at the SUNY Downstate Medical Center ...
The conjoint longitudinal muscle is a muscle layer in the wall of the anal canal between the internal anal sphincter (deep to CLM) and external anal sphincter (superficial to CLM). It is continuous proximally with the longitudinal (outer) smooth muscle layer of the rectum. It receives autonomic innervation in common with the internal anal ...